Automatic traction control system

ABSTRACT

A wheel traction control system is disclosed which automatically detects a maximum-traction wheel slippage and controls brake and drive systems so as to maintain this maximum-traction wheel slippage. The system essentially includes a wheel slippage detector, an automatic braking control device and an automatic accelerating control device. The wheel slippage detector comprises an angular accelerometer and a linear accelerometer, which press against one another to measure the ratio of wheel angular acceleration to vehicular linear acceleration. If wheel slippage is caused by vehicular &#39;&#39;&#39;&#39;braking action&#39;&#39;&#39;&#39;, the wheel slippage detector sends a control signal to the automatic braking control device and if wheel slippage is caused by vehicular &#39;&#39;&#39;&#39;accelerating action&#39;&#39;&#39;&#39;, the wheel slippage detector sends a control signal to the automatic accelerating control device. The automatic braking control device includes a brake-fluid line valve which is biased toward the closed position but which is opened by brake-fluid flow in the direction of a wheel cylinder. Further, the valve is closed tightly in response to a signal from the wheel slippage detector. The automatic accelerating control device includes an oscillator and a relay. Essentially, the accelerating control device responds to a slippage-detector signal by intermittently interrupting a vehicle&#39;&#39;s ignition circuit. Safety devices are also included to deactivate the wheel traction control system in the event of malfunctions.

United States Patent [1 1 Barthlome [111 3,744,850 July 10, 1973 1AUTOMATIC TRACTION CONTROL SYSTEM [76] Inventor: Bonaldll. Barthlome,313 Orange Plank Road, Hampton, Va. 23369 [22] Filed: Mar. 8, 1971 [21]Appl. No.: 122,009

[52] 11.5. CI 303/21 B, 188/181 A, 303/21 F [51] Int. Cl B60t 8/12 [58]Field of Search 73/510; 188/181, l88/349y303/20, 6 C, 21; 324/162;340/262; 317/5 [56] References Cited UNITED STATES PATENTS 3,066,98812/1962 McRae 303/21 F UX 3,224,278 12/1965 303/21 B UX 3,292,977 12/1966 Williams 303/21 B 3,401,984 9/1968 Williams et a]. 303121 BE3,402,973 9/1968 Scibbe 303/21 BB 3,506,312 4/ 1970 Siddall 188/349 X3,554,613 l/197l Fiscus et al. 303/21 B 3,582,152 6/1971 Burckhardt et303/21 EB 3,608,978 9/1971 Neisch 303/21 EB 3,512,844 5/1970 Stelzer303/21 F Primary Examiner-Duane A. Reger Assistant Examiner-Stephen G.Kunin Attorney-Griffin, Branigan and Kindness [57 ABSTRACT A wheeltraction control system is disclosed which automatically detects amaximum-traction wheel slippage and controls brake and drive systems soas to maintain this maximum-traction wheel slippage. The systemessentially includes a wheel slippage detector, an automatic brakingcontrol device and an automatic accelerating control device. The wheelslippage detector comprises an angular accelerometer and a linearaccelerometer, which press against one another to measure the ratio ofwheel angular acceleration to vehicular linear acceleration. lf wheelslippage is caused by vehicular braking action, the wheel slippagedetector sends a control signal to the automatic braking control deviceand if wheel slippage is caused by vehicular accelerating action, thewheel slippage detector sends a control signal to the automaticaccelerating control device. The automatic braking control deviceincludes a brakefluid line valve which is biased toward the closedposition but which is opened by brake-fluid flow in the direction of awheel cylinder. Further, the valve is closed tightly in response to asignal from the wheel slippage detector. The automatic acceleratingcontrol device includes an oscillator and a relay. Essentially, theaccelerating control device responds to a slippage-detector signal byintermittently interrupting a vehicles ignition circuit. Safety devicesare also included to deactivate the wheel traction control system in theevent of malfunctions.

11 Claims, 10 Drawing Figures United States Patent L 1 [111 3,744,850Barthlome July 10, 1973 SIIEHZNS llllllll NVEN TOR.

FIGS

SHEUSGFS INVENTOR DGIALD E.BARTHLOME QT QMEvs AUTOMATIC TRACTION CONTROLSYSTEM This invention relates generally to the artof automatic wheeltraction control systems and, in particular, it provides a system whichis capable of responding to wheel slippage caused by either vehicularbraking action or vehicular accelerating action.

it is well known that the efficiency with which a vehicle is braked oraccelerated is highly dependent upon wheel slippage. In this regard,with reference to FIG. 1, a typical braking tire-to-roadcoefficient-of-friction characteristic for a vehicle on dry asphalt isshown plotted versus both percent slip and time. The time data shown onthis plot is estimated and intended for illustrative purposes only. Fromthis characteristic curve it can be seen that maximum braking efficiencyis obtained when the degree of wheel slippage reaches a value just tothe left of the peak of the curve. In this regard, the slip to the leftof the peak is due to elastic deformation of a tire whereas the slip tothe right of the peak is due primarily to sliding of the tire on a roadsurface. With this in mind, the wheel slippage magnitude of the maximumbreaking efficiency (MBE) slip can vary depending on conditions. Forexample, when braking on dry concrete tires can distort so severly as topermit a MBE slip as high as to percent whereas on wet asphalt thedistortion may be only 8 or 9 percent. Braking on packed snow and icewill produce virtually no tire distortion. The time required to reachthe MBE slip during a panic stop is estimated to be approximately 0.01of a second on dry asphalt, as measured from the time a brake liningcontacts a brake drum. It is desirable to design automatic tractioncontrol systems to sense when wheel slippage reaches this maximumtraction efficiency point, regardless of its magnitude, and tothereafter maintain this wheel slippage.

Most prior art automatic braking control systems do not possess thefollowing capabilities: (I) the ability to respond when a near maximumbraking efficiency wheel slippage is reached regardless of itsmagnitude, (2) the ability to instantly stabilize brake pressure whenthe near maximum degree of wheel slippage is reached, and (3) theability to maintain the brake pressure constant throughout the timeduration of a panic stop. Most prior art systems, after sensing thatwheel slippage has exceeded some maximum fixed value, introduce acontrolled pumping action similar to the pumping of a brake pedal by adriver. in this manner, the degree of wheel slippage is made tocontinually rise above and fall below the maximum braking efficiencypoint, as typically indicated in FIG. 1, for braking action on dryasphalt. An example of this type of system is described in U.S. Pat. No.3,301,608 to Harned et al. One difficulty with such systems is that theycannot take full advantage of the maximum braking efficiency point.Also, it is generally known that the application of a constant pressureon a brake pedal produces a much more effective braking action than doesan intermittent or pumping" type action. Therefore, it is an object ofthis invention to provide an automatic braking control system which canrespond when some maximum desirable degree of slip is reached and thento lock brake-fluid pressure so as to maintain this degree of slippagethroughout a panic stop.

Because they produce a pumping action" most prior art automatic brakingcontrol systems provide noticeable responses which are sensed by driversor passengers of vehicles. Such responses can be distracting to driversand, therefore, can be dangerous. It is therefore yet another object ofthis invention to provide an automatic traction control system theoperation of which is not distracting either to drivers or passengers.

In addition, some prior art systems do not provide slippage detectionand control for all four wheels. A primary reason for this limitation isthat a four wheel system is too expensive. For example, in some suchsystems the slippage of only one or two wheels may cause a reduction ofbrake-fluid pressure simultaneously at all four wheels. Or, in othersuch systems, two wheels must slip before the systems are activated.Such systems clearly do not provide the flexibility required to obtainnear maximum braking efficiency for all four wheels. Therefore, it isanother object of this invention to provide an automatic braking systemwhich has separate detecting units for each wheel and separate controlunits for each set of front and rear wheels, but yet which iseconomically practical.

Although some prior art automatic traction control systems havedetectors which respond to wheel slippage arising from either excessivevehicular braking action" or excessive vehicular accelerating action,few systems have one detector for detecting both types of wheelslippage. Accordingly, it is an object of this invention to provide anautomatic traction control system having a slippage detector fordetecting wheel slippage, arising from either excessive braking actionor excessive accelerating action and providing control signals which arecharacteristic of each of these types of slippages.

Still another disadvantage with many prior art automatic tractioncontrol systems is that they are somewhat unsafe. That is, they do nothave sufficient mechanisms to protect against wheel lock caused bysystem malfunctions. Therefore, it is another object of this inventionto provide a system which has a built-in safety margin againstmalfunctions.

Yet another problem with some prior art automatic traction controlsystems is that their wheel slippage detectors are unduly complex. Forexample, in some such prior art systems an electronic comparator circuitmust be employed to compare a vehicular linear acceleration signal witha wheel angular acceleration signal. It is therefore another object ofthis invention to provide an automatic traction control system having awheel slippage detector which is not unduly complex.

SUMMARY OF THE INVENTION According to the principles of this inventionan automatic traction control system has a fast-response wheel-slippagedetector for providing control signals to both an automatic brakingcontrol system and an automatic accelerating control system.

Generally, the slippage detector includes a sensor unit made up of awheel angular accelerometer and a wheel linear accelerometer, whichtogether measure the ratio of angular acceleration to linearacceleration. The accelerometers press against one another, eachpressing with a force proportional to the acceleration it is measuring.When the vehicle accelerates, the pressing force of one accelerometerovercomes that of the other accelerometer producing a physicaldisplacement of accelerometers. When this displacement reaches apredetermined magnitude a measuring means in the detector provides aslippage warning signal to either the automatic braking control systemor the automatic accelerating control system, depending on whether thewheel slippage is caused by vehicular braking action or acceleratingaction. The slippage detector responds virtually instantaneously to themaximum-traction-efficiency slippage, regardless of its magnitude.

The automatic braking control system comprises a brakefluid lockingdevice. In the preferred embodiment the locking device is a solenoidactuated valve. A significant feature of the valve is that its plungeris normally biased in the closed position but can ordinarily be openedby brake fluid flow in the direction of a wheel cylinder when a vehicles brakes are applied. However, when the valve receives aslippage-warning signal from the slippage detector the plunger is forcedtoward a closed position and brake fluid can no longer flow through thevalve. The valve has an unusually quick response time by virtue of thefact that actual brake-fluid flow ceases as soon as a brake liningcontacts a brake drum; thus, when the valve receives a slippage warningsignal the plunger has already moved to an almost closed position. Whenthe brake is released brake fluid is allowed to flow around the valve,through a bypass line and check valve.

Essentially, the cumulative response time of the slippage detector andthe automatic braking system is fast enough so that the automaticbraking system can lock the brake system of a vehicle at a wheelslippage closely corresponding to the maximum braking efficiency(M.B.E.) slippage detected by the slipppage detector.

The particular automatic accelerating control system employed in thisinvention is old in the art. Generally this system controls a vehiclesacceleration by intermittently interrupting the vehicles ignitioncircuit in response to a slippage warning signal.

The automatic traction control system of this invention also includessafety devices which deactivate the automatic braking and acceleratingcontrol systems in the event of malfunctions.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects,features and advantages of the invention will be apparent from thefollowing more particular description of the preferred embodiment of theinvention, as illustrated in the accompanying drawings in whichreference characters refer to the same parts throughout the differentviews. The drawings are not necessarily to scale, emphasis instead beingplaced upon illustrating the principles of the invention in a clearmanner.

FIG. 1 is a graphical representation of a typicalcoefficient-of-friction characteristic of a vehicle's wheel;

FIG. 2 is a simplified block diagram representing an automatic tractioncontrol system employing principles of this invention;

FIG. 3, is a schematic representation of an automatic traction controlsystem employing principles of this invention;

FIG. 4 is a simplified isometric view of a wheelslippage-detector sensorunit which employs principles of this invention;

FIGS. 5 and 6 are sectional views of portions of the sensor unit of FIG.4 when it is not preloaded for operation;

FIGS. 7a and 7b are close-up views of portions of the sensor unit shownin FIG. 4 when it is preloaded for operation;

FIG. 8 is a front sectional view of the slippage deter. tor of FIG. 9;taken along line 8-8; and,

FIG. 9 is a partially cutaway side view of a slippage detector employingprinciples of this invention, showing in some detail the measuring meanstherefor.

DESCRIPTION OF THE PREFERRED EMBODIMENT For purposes of orientation,reference is first made to the block diagram in FIG. 2 wherein is shownan automatic traction control system mounted on a vehicle 10 havingwheels 12, a motor 14, a drive shaft 16, a differential 18, a back axle20, front axles 22, a brake pedal 24, a master cylinder 26, brake-fluidlines 28fand 28r, and four brake housings 34 a-d.

The automatic traction control system includes: four slippage detectors36 a-d (one mounted in each of the brake housings 34 a-d), two automaticbraking control systems (brake-fluid locking devices) 38f and 38r, twocheck valves 40f and 40r with associated bypass lines 42 f and 42r, andan automatic accelerating control system 44.

A front brake fluid locking device 38f is connected in the brake fluidline 28f between the master cylinder 26 and the front brake housings 34a and d. A rear brake fluid locking device 38r is connected in the brakefluid line 28r between the master cylinder 26 and the rear brakehousings 34b and 0. Further, each of the check valves 40, with itsassociated bypass line 42 respectively provides a bypass around one ofthe brake fluid locking devices 38. Each of the slippage detectors 36 ismounted in a brake housing 34 so as to detect wheel slippage. Theslippage detectors 36 on the front and rear wheels are electricallyconnected to the brake fluid locking devices 38 by brake signal lines46f and r respectively. In addition, each of the back wheel slippagedetectors 36 b and c is connected to the automatic accelerating controlsystem 44 by a respective one of the acceleration lines 48 b and c.

Turning now to the operation of the simplified system illustrated inFIG. 2, when the brake pedal 24 is depressed the master cylinder 26causes pressure to increase in the brake-fluid lines. This pressure istransmitted through the brake fluid locking devices 38 and the front andrear brake fluid lines 28 f and r to brake linings (not shown) in thebrake housings 34. When the brake pedal 24 is released, brake fluid isallowed to return to the master cylinder 26 through the check valves 40and the bypass lines 42.

Now assume that a driver depresses the brake pedal 24 violently. Whenthe brake fluid pressure is transmitted to the brake linings (notshown), as is described above, the rotation of wheels 12 deceleratesrapidly and the wheels begin to slip in accordance with thecharacteristic curve shown in FIG. 1. When the degree of wheel slippagereaches maximum braking efficiency the slippage detectors 36 a-d(assuming all wheels are slipping in the same manner under similarconditions) detect that the maximum-braking-efficiency slippage has beenreached and independently signal the brake fluid locking devices 38 fandr to that effect. The brake fluid locking devices 38 f and r lock thebrake fluid line 28 so that the brake fluid pressures, as seen at thebrake linings in the brake housings 34, are locked at pressures closelycorresponding to the pressures which caused themaximum-braking-efflciency slippage. Thus, once the automatic brakingsystem goes into effect, the brakes are locked near themaximum-brakingefficiency wheel slippage.

The slippage detectors 36 of this invention (described in detail below)and the brake fluid locking devices 38 (also described in detail below)have extremely short response times and therefore enable the generalsystem shown in FIG. 2 to operate as described above.

The back wheel slippage detectors 36 b and c provide accelerationslippage signals, on the acceleration signal lines 48 b and c, to theautomatic accelerating control system 44. The automatic acceleratingcontrol system 44, in turn, controls the rate at which the motor 14causes the back wheels 12 to accelerate. More particularly, when a caris accelerated too rapidly and its back wheel slippage nears themaximum-accelerating-efficiency slippage (similar to themaximum-braking-efficiency slippage shown in FIG. 1) the slippagedetectors 36 b and 0 independently provide signals to the automaticaccelerating control system 44. The automatic accelerating controlsystem 44 controls the motor 14 which in turn reduces the powerdelivered to the back wheels 12 in a manner to be described below.

Referring next to the FIG. 3 schematic representation of part of thesame automatic traction control system shown in FIG. 2 with additionalelements added, there is shown one of the slippage detectors 36(represented by dashed lines and shown in more detail in FIGS. 49), oneof the brake fluid locking devices 38, one of the check valves 40 withits associated bypass line 42, and the automatic accelerating controlsystem 44. Additional elements of the automatic traction control systemshown in FIG. 3, but not shown in FIG. 2, are various elements ofelectrical circuitry (to be described below) which include safetyswitches (braking system safety switch 49 and accelerating system safetyswitch 51). Elements of a vehicle shown in FIG. 3 include: the brakepedal 24, the master cylinder 26, the brake fluid line 28, a brakehousing 34, an accelerator pedal 53, and the motor 14 (represented bydashed lines) with an ignition coil 55 and a distributor 57.

Describing firstly the automatic braking control system of FIG. 3, thecheck valve 40 includes a check valve seat 50, a check valve poppet 52and a check valve biasing spring 54. The biasing spring 54 normallybiases the check valve poppet 52 in a closed position. Flow of brakefluid from the master cylinder 26 toward the brake housing 34 isprevented from going through the bypass line 42 by the valve poppet 52,however, brake fluid flowing from the brake housing 34 toward the mastercylinder 26 overcomes the check valve biasing springs tension andthereby unseats the check valve poppet 52.

The brake fluid locking device 38 essentially comprises a solenoid coil56, a plunger 58, a solenoid valve seat 60, and s solenoid valvesupporting spring 62. The plunger 58 is normally held in a seatedposition against the solenoid valve seat 60 by its own weight. However,a flow of brake fluid from the master cylinder 26 toward the brakehousing 34 unseats the plunger 58; thus, allowing flow of brake fluidaway from the master cylinder 26 through the brake fluid locking device38. The support spring 62 provides lift to the plunger 58, therebycreating a desired sensitivity of plunger movement to fluid flow. Thus,fluid flow away from the master cylinder 26 is through the brake fluidlocking device 38 and brake fluid flow toward the master cylinder isthrough the bypass line 42.

When the solenoid coil 56 is energized the plunger 58 is pressed tightlyagainst the solenoid valve seat 60 thereby preventing flow of brakefluid from the master cylinder 26 toward the brake housing 34 throughthe brake fluid locking device 38.

It can be seen in FIG. 3 that the slippage detector 36 comprises abraking magnetic reed switch 64 having two contacts 65 a and b and anaccelerating magnetic reed switch 66 having two contacts 67 a and b.Also included in the slippage detector is a slippage sensor unit whichis shown in more detail in FIGS. 4-9 but which is not included in FIG.3. The slippage sensor unit causes movement of a magnet (not shown inFIG. 3) in response to the maximum traction wheel slippage so as toactivate either the braking reed sensor switch 64 or the acceleratingmagnetic reed switch 66.

Operation of the FIG. 3 automatic braking system is as follows: As thebrake pedal 24 is depressed the master cylinder 26 causes an increase inpressure in the brake line 28. At the same time, brake fluid flowsthrough the check valve 40 to the brake fluid locking device 38. Theplunger 58, which is seated under the action of its own weight, isforced away from the valve seat 60 by brake fluid flow. However, oncethere is sufficient brake fluid pressure to cause a brake lining (notshown) to contact a brake drum (not shown) in the brake housing 34,brake fluid flow through the brake fluid locking device 38 ceases andthe plunger 58 settles back toward the valve seat 60. If the brake pedal24 is released, brake fluid flows from the brake housing 34 toward themaster cylinder 26 through the bypass line 42 and the check valve 40.

Now suppose the brake pedal 24 is depressed violently for a panic stop.Brake fluid pressure is transmitted to the brake lining (not shown) inthe brake housing 34 as was described above. Once the brake lining (notshown) contacts the brake drum (not shown) the wheels of a vehicle beginto slow down and to slip on pavement in accordance with the wheelslippage characteristic curve shown in FIG. 1. At zero time of FIG. 1brake fluid flow through the brake fluid locking device 38 essentiallyceases and the plunger 58 begins to settle back toward the solenoidvalve seat 60. By the time the wheel slippage has reached a desirabledegree of slip the plunger 58 is again seated, or close to being seated,on the valve seat 60. Very near this desirable wheel slippage thesolenoid coil 56 is energized in response to a slippage warning signalfrom the slippage detector 36 (the energizing circuit and slippagedetector are described below) and the plunger is held tightly againstthe solenoid valve seat 60, thus, locking the braking system near adegree of wheel slippage which produces maximum braking efficiency.

It can be appreciated by those skilled in the art that the brake fluidlocking device 38 has an extremely short response time due to the factthat the plunger is actually seated, or almost seated, prior toactivation of the locking device. A significant structural feature ofthe brake fluid locking device 38 is the biased plunger, which is biasedtoward a seated position, but yet which is opened by brake fluid flowfrom the master cylinder toward the brake lining as long as the solenoidcoil 56 is not energized.

Turning secondly to the automatic accelerating control system 44 of FIG.3, this system is connected to the ignition coil 55 of the motor 14. Theignition coil 55 is connected directly to the spark plugs (not shown) ofthe motor 14 and to ground through the contact breaker (not shown) ofthe distributor 57. The automatic accelerating control system 44 is oldin the art and therefore not shown in detail in FIG. 3. This systemincludes mainly a voltage controlled oscillator and an electromechanicalrelay for intermittently interrupting current flowingto the ignitioncoil 55.

Briefly, activation of the accelerating magnetic reed switch 66, inresponse to a desirable wheel slippage, activates the automaticaccelerating control system 44 which, in turn, operates on the ignitioncircuit to control the power output of the motor 14.

Turning thirdly to the electrical circuitry of FIG. 3, including thesafety switches, the circuitry is made up of a braking-system circuitand an acclerating-system circuit.

The braking system circuit includes the voltage source 72, the brakingsensor reed switch 64, an energizing relay 74, a safety relay 76, thebraking safety switch 49, amalfunction alarm light 80, and a brake pedalswitch 82 (which is a part of the master cylinder 26).

The voltage source 72 is a vehicle battery.

The energizing relay 74 is a solid state relay having two controlterminals 84 a and b and two transmission terminals 86 a and b.

Likewise, the safety relay 76 is a solid state relay having two controlterminals 88 a and b and two transmission terminals 90 a and b. Therelays 74 and 76 are constructed such that when a current flows throughthe control terminals 84 a and b 88 a and b circuits are respectivelycompleted through the transmission terminals 86 a and b and 90 a and b.

The braking safety switch 49 comprises four stationary contacts 92 a-d,two electrically-interconnected movable contacts 94, a plunger 96, amagnetic plunger retaining means 98, an armature 100, a solenoid coil102, a biasing spring 104, a push button 106, and a permanent retainingmagnet 108. The plunger 96 is normally biased by the biasing spring 104such that movable interconnected contacts 94 are respectively in contactwith the third and fourth stationary contacts 92 a and d. Energizing thesolenoid coil 102 causes the armature 100 and the attached plunger 96 tomove to the right as seen in FIG. 3. However, as the plunger 96 moves tothe right the movable contacts 94 continue to make contact at first withthe first and fourth stationary contacts 92 aand b, due to theresilience of an interconnecting member 110. Finally, the magneticplunger retaining means 98 comes under the influence of the permanentretaining magnet 108, at which point, the movable contacts 94 breakcontact with the first and fourth stationary contacts 92 a and d. Oncethe movable contacts 94 make contact with the second and thirdstationary contacts 92 b and c, the braking safety switch 49 is held inthis position by the permanent retaining magnet 108 until an externalforce is applied to the push button 106.

The brake pedal switch 82 comprises four stationary contacts 112 a-d andtwo electrically-interconnected movable contacts 114. When no force isapplied to the brake pedal 24 the movable contacts 114 are respectivelyin contact with the second and third stationary contacts 112 b and 0.However, when a force is applied to the brake pedal 24 the movablecontacts 114 are moved into respective contact with the first and fourthstationary contacts 112 a and d.

The malfunction alarm light is connected between the third stationarycontact 92 c of the safety switch 49 and ground, and is located on avehicle 5 dashboard.

Tracing the circuit of the automatic brake control system, the voltagesource 72 is connected to the first contact 65a of the reed switch 64.The second reed switch contact 65b is connected to the first controlterminals 84a of the energizing relay 74 and the second control terminal84b is connected to the first control terminal 88a of the safety relay76. The second control terminal 88b of the safety relay is coupled tothe first safety switch stationary contact 92a and the fourth stationarycontact 92d is connected to ground.

The voltage source 72 is also connected directly to the brake pedalswitchs first and second stationary contacts 112a and ll2b. The brakepedal switchs fourth stationary contact 112d is connected to the secondtransmission terminal 86b of the energizing relay 74 and the firsttransmission terminal 86a is coupled through the locking-device solenoidcoil 56 to ground. The brake pedal switchs third stationary contact 112cis connected to the first transmission terminal a of the safety relay 76and the second transmission terminal 90b is connected through thesafety-switch solenoid coil 102 to ground.

Further, the voltage source 72 is connected through a vehicle ignitionswitch 116, which is closed when the vehicle is in operation, to thesafety switchs second stationary contact 92b. The third stationarycontact 92c of the safety switch 49 is connected through the malfunctionalarm light 80 to ground.

Now describing the operation of the part of the braking system circuitwhich energizes the solenoid coil 56, as the brake pedal 24 isdepressed, the movable contacts 114 of the brake pedal switch 82 areseparated from the second and third stationary contacts 112 b and c andbrought into contact with the first and fourth stationary contacts 112 aand d. If the wheels of a vehicle begin to slip, and the degree ofslippage approaches that which provides maximum braking efficiency, aslippage sensor unit (which is a part of the slippage detector 36, butnot shown in FIG. 3) brings a permanent magnet in close proximity to thebraking magnetic reed switch 64 and thereby causes the reed switchcontacts 65 a and b to close. Once the reed switchs contacts 65 areclosed current flows between the control terminals 84 a and b of theenergizing relay 74 thereby completing the circuit between thetransmission terminals 86 of the energizing relay 74. Thus, a circuit iscompleted from the voltage source 72 through the solenoid coil 56 andthe plunger 58 is thereby driven downwardly.

Next describing the operation of the safety part of the braking systemcircuit which deactivates the automatic braking control system in theevent of a malfunction, closing the reed switch contacts 65 (asdescribed above), in addition to activating the energizing relay 74,also causes a current between the control terminals 88 of the brakingsafety relay 76. This, in turn, closes the circuit between thetransmission terminals 90 of the safety relay 76. However, the solenoidcoil 102 of the braking safety switch 49 is not thereby energizedbecause the brake pedal switchs second and third stationary contacts 112b and c are open. However, suppose the brake pedal is released but yetthe reed contacts 65 of the reed switch 64 improperly remain in a closedcondition. Current now flows between the second and third stationarycontacts 112 b and c due to the electrically-interconnected movablecontacts 114 thereby energizing the solenoid coil 102, which in turn,causes the armature 100, and its attached plunger 96, to be moved to theright, as seen in FIG. 3, against the force of the biasing spring 104.Movement of the plunger 96 opens the first and fourth stationarycontacts 92 a and d and closes the second and third stationary contacts92 b and 0. First and fourth contacts 92 a and d, however, must remainclosed until the magnetic plunger retaining means 98 is sufficientlyattracted by the permanent retaining magnet 108 to insure closure of thesecond and third stationary contacts 92 b and c. This is provided by abuilt-in resilience in the interconnecting member 110 of theelectrically-connected movable contacts 94 as was described above. Theclosure of the second and third stationary contacts 92 b and c permitscurrent to flow from the voltage source 72 through the ignition switch116 to the braking system malfunction alarm light 80, which is mountedon the vehicles dashboard.

In a similar manner, opening the first and fourth stationary contacts 92a and d deenergizes the solenoid coil energizing relay 74 and therebyopens the circuit to the solenoid coil 56 of the brake fluid lockingdevice 38. Thus, the brake fluid locking device 38 is disabled.

Likewise, should the braking magnetic reed switch 64 be improperlyactivated by forces other than those arising from a braking action, thesecond and third stationary contacts 112 b and c of the brake pedalswitch 82 will be in a closed position and the sequence of events willbe identical to those described in the preceding paragraph, thusresulting in activation of the brake system malfunction alarm light 80and disabling of the locking device 38.

Thereafter, in either case, the braking system safety switch 49 is heldin a safe position by the permanent retaining magnet 108 until theplunger 96 is pushed to the left as seen in FIG. 3 by pushing the pushbutton 106 manually. When the braking system safety switch 49 is in thesafe position the braking systems functions as a conventional manualbraking system.

The automatic accelerating system control circuit is much the same asthe automatic braking system control circuit and essentially comprises:the voltage source 72 (described previously), the acceleration sensorreed switch 66 (described previous y), an energizing relay 118, a safetyrelay 120, the safety switch 51, a malfunction alarm light 124, and anaccelerator pedal switch 125.

The energizing relay 118 is a solid state relay which has two controlterminals 126 a and b and two transmission terminals 128 a and b.

Likewise, the safety relay 120 is a solid state relay which has twocontrol terminals 130 a and b and two transmission terminals 132 a andb.

The accelerating system safety switch 51 is identical to the brakingsystem safety switch 49 in both structure and operation, as wasdescribed above, however, for ease of reference the elements thereof aregiven numerical designations as follows: four stationary contacts 134a-d, two electrically-interconnected movable contacts 136, a plunger138, a magnetic plunger retaining means 140, an armature 142, a solenoidcoil 144,

-a biasing spring 146, a push button 148 and a permanent retainingmagnet 150.

The accelerator switch 125 includes two stationary contacts, 152 a andb, v and two electricallyinterconnected movable contacts 154. Themovable contacts 154 are linked with an accelerator pedal 53 such thatwhen the accelerator pedal 53 is not depressed the movable contacts 154are respectively in contact with the first and second stationarycontacts 152 a and b; however, when the accelerator pedal 53 isdepressed, the movable contacts 154 are taken out of contact with thestationary contacts 152 a and b.

Tracing the automatic accelerating control system circuit, the voltagesource 72 is connected to the first reed contact 67a of the slippagesensor switch 66. The second reed contact 67b of the slippage sensorswitch 66 is connected through the control terminals 126 of theoscillator energizing relay 118 and the control terminals 130 of thesafety relay to the fourth stationary contact 134d of the safety switch51. The first stationary contact 134a of the safety switch 51 isconnected to ground.

Further, the voltage source 72 is connected to the second transmissionterminal 128b of the energizing relay 118 and the first transmissionterminal 128a of the energizing relay 118 is connected to the automaticaccelerating control system 44. The automatic accelerating controlsystem 44 is, in turn, connected through the vehicle ignition coil 55and the distributor 57 to ground. The automatic accelerating controlsystem 44 also is coupled directly to the power source 72 through thevehicle ignition switch 116.

In addition, the power source 72 is coupled to the second stationarycontact l52b of the accelerator switch 125. The first stationary contact1520 of the accelerator switch is connected to the second transmissionterminal 132b of the safety relay 120, and the first transmissionterminal 132a of the safety relay 120 is connected through the safetyswitch solenoid coil 144 to ground.

The voltage source 72 is further connected through the ignition switch116 to the third stationary contact 134C of the safety switch 51. Thesecond stationary contact l34b of the safety switch 51 is connectedthrough the malfunction alarm light 124 to ground.

Now describing the operation of the part of the accelerating controlcircuit of FIG. 3 which energizes the automatic drive system 44, as theaccelerator pedal 53 is depressed the wheels of a vehicle are caused toaccelerate and thereby to slip on a pavement. When the degree of wheelslippage nears the point of maximum traction efficiency, similar to thatshown in FIG. 1, a slippage sensor unit (to be described below inconjunction with FIGS. 4-9) of a slippage detector 36 brings a magnetadjacent to the accelerating magnetic reed switch 66, thereby closingthe reed contacts 67. Closure of these contacts activate the oscillatorenergizing relay 118 thereby allowing current flow from the voltagesource 72 through the transmission terminals 128 to the automatic drivesystem 44, which comprises primarily a voltage controlled oscillator(not shown) and an electromechanical relay (not shown). The voltagecontrolled oscillator of the automatic drive system 44 is turned on bythe signal it receives through the transmission terminals 128 a and band it, in turn, causes an electromechanical relay (not shown) tointerrupt current flowing through it from the voltage source 72 throughthe ignition switch 116 to the ignition coil 55 and the distributor 57.

The oscillator (not shown) produces a 50 cycle/- second square wavesignal which causes the electromechanical relay (not shown) to make andbreak the ignition circuit approximately once every ten milliseconds. Bythusly controlling the current flowing to the coil 55, the distributor57, and spark plugs (not shown) the power of the motor 14 is alsocontrolled so as to maintain a desirable wheel slippage condition.

With regard to operation of the safety part of the acclerating systemcircuit, if the accelerator pedal 53 is released thereby closing theaccelerator switch 125, but the slippage sensor unit (not shown in FIG.3) improperly continues to close the reed contacts 67 a and b, thesolenoid coil 144 of the safety switch 51 is activated by a currentflowing from the voltage source 72 through the accelerator switch 125and the safety relay 120. The automatic acceleration control system isthereby deactivated in the same manner as was the automatic brakingcontrol system described above.

Turning now to the actual slippage sensor elements of the slippagedetectors 36 shown in FIGS. 2 and 3, reference is made to FIGS. 4-9.FIGS. 4-7 illustrate a simplified slippage sensor unit 158. The sensorunit 158 comprises essentially a rotational mass 160, rotationalmasssprings 162, a rotationalmass mounting plate 164 attached to a wheel165, a linear mass 166, linear mass springs 168, a linear mass mountingplate 170 attached to a vehicles frame 171, and a bearing assembly 172.

The flat, rectangularly shaped, rotational-mass springs 162 are radiallyoriented between the rotational-mass mounting plate 164 and therotational mass 160 and are attached to both these members. Thelinear-mass springs 168 are oriented in vertical parallel planes and areattached between the linear-mass 166 and the linear-mass mounting plate170. Again, it should be particularly noted that the rotational-masssprings 162 are mounted in radially disposed planes whereas thelinear-mass springs 168 are mounted in parallel vertical planes.

The rotational-mass mounting plate 164 is attached to a rotating memberof a wheel 165 and rotates therewith. The rotational mass 160 is therebycaused to rotate through the rotational mass springs 162. Thelinear-mass mounting plate 170, on the other hand, is affixed to anon-rotating member of a vehicle s frame 171 and therefore this member,as well as the linear mass 166, does not rotate. The rotational-massmounting plate 164 and the linear-mass mounting plate 170 are pushedtoward one another by a static force indicated by arrows 177 which iscreated when the slippage sensor unit 158 is mounted on a vehicle aswill be explained in more detail below. The static force 177 causes thelinear-mass springs 168 and the rotationalmass springs 162 to bend as isshown in FIG. 4 so that the rotational mass 160 is angularly displacedin a counter clockwise direction (as seen in FIG. 4) from therotational-mass mounting plate 164. This displacement can be moreclearly seen in FIGS. 7a and 7b wherein it is represented by the letterA. The linear mass 166 is linearly displaced to the left (as seen inFIG. 4) from the linear-mass mounting plate 170. Thus, the springs 162and 168 are preloaded and cause the masses 160 and 166 to press againstone another through the bearing assembly 172.

The bearing assembly 172 allows both relative rotational and linearmotion between the rotational mass and the linear mass 166. I

There are two switching magnets, a braking switching magnet 180 and anaccelerating switching'magnet 182 respectively mounted on the top andbottom of the linear mass 166. These magnets cooperate with the slippagereed sensor switches 64 and 66 (FIG. 3) as will be described shortly.

FIGS. 5 and 6 show'the manner in which the rotationalmass springs andthe linear-mass springs are mounted to their respective mounting platesand masses. As can be seen, the springsl62 and 168 are wedged in a slot181 by rectangularly shaped wedge members 183. The wedge members 183 areheld in position by nuts and bolts 185.

Turning now to the operation of the simplified slippage sensor elementshown in FIGS. 4-7, as the vehieles wheel rotates the rotational-massmounting plate 164 and the rotational mass 160 also rotate; however, thelinear-mass mounting plate and the linear-mass 166 are held stationaryby the vehicles frame 171. During periods of no wheel slippage when thevelocity of the vehicle is constant, the rotational mass 160 and thelinear mass 166 press against one another through the bearing assembly172 with equal and opposite forces created by preloaded tensions in therotational-mass springs 162 and the linear-mass springs 168.

Before the brakes of the vehicle are applied, the configuration of thesprings 162 and 168 are as shown in FIG. 70. At this time the magnitudeof the inertial forces F and F is zero. At the instant the brake liningcontacts the brake drums, the vehicle begins to decelerate and F and Falong with the degree of wheel slip, begin to increase in magnitude. Asthe values of F and F increase, their relationship is such as to causethe linear mass 166 and its attached switching magnet to move to theleft as shown in FIG. 7b. As indicated, this movement increasesdimension A for linear mass 166 and decreases dimension A for rotationalmass 160 (dimension A having a static value of approximately 0.033inches). A continued increase in vehicular deceleration, with anassociated increase in wheel slip, produces a continued increase in therelative displacement of the masses 166 and 160 as shown in FIG. 7b. Ifthe ratio of F and F should now reach a critical magnitude the wheelwill have reached, or nearly reached, a degree of slip corresponding tothe point of maximum braking efiiciency (see FIG. 1). When thiscondition exists, linear mass 166 and switching magnet 180 will havebeen displaced sufficiently so as to activate reed switch 64 therebycreating a slippage signal which activates the brake fluid lockingdevice 38 shown in FIG. 3 and described above. The change in A from theinstant deceleration begins until reed switch 64 is activated (shown asA A in FIG. 7b) is exaggerated in FIG. 7b for illustrative purposesonly. The total movement of each of the sensing masses is quite small,i.e., between 0.004 and 0.005 of an inch.

If, rather than braked, a vehicle is suddenly accelerated therebycausing wheel slippage the linear mass 166, and the attached switchingmagnet 182, (shown in FIG. 4) move to the right thereby activating theaccelerating magnetic reed switch 66 (shown in FIG. 3 but not shown inFIG. 4) and creating a slippage signal which activates the automaticaccelerating control system 44 shown in FIG. 3.

FIGS. 8 and 9 show a practical embodiment of the slippage sensor elementof FIGS. 4-7. Referring to FIG. 8, and using the same correspondingreference numerals as were used in FIGS. 4-7, even through the elementsthemselves may appear to be somewhat different in structure, theslippage sensor element 158 comprises a rotational mass 160, rotationalmass springs 162, a rotational-mass mounting plate 164, a linear mass166, linear mass springs 168, a linear-mass mounting plate 170, and abearing assembly which includes a rotation bearing 184, a linear bearing186 and a mounting plate bearing 188. As in the FIG. 4 embodiment, aswitching magnet 180 is mounted at the top of the linear mass 166 and aswitching magnet 182 is located at.the bottom of the linear mass 166.The braking magnetic reed switch 64 (shown in the circuit in FIG. 3) ismounted on the linear-mass mounting plate 170 by a rivet 190 adjacent tothe braking switching magnet 180. The accelerating magnetic reed switch66 (shown in more detail in FIG. 3) is mounted on the linear-massmounting plate 170 adjacent to the accelerating switching magnet 182.

The linear-mass mounting plate 170 is fixedly attached to a vehicle (notshown in FIG. 8) by a pin 192; thus, preventing rotation of thelinear-mass mounting plate 170, the linear-mass springs 168, and thelinearmass 166 with attached switching magnets 180 and 182. Therotational-mass mounting plate 164, on the other hand, is fittedsecurely over the hub of a front brake drum (for a front wheel) or overthe axle shaft (for a rear wheel) so that it rotates with the wheel.Also caused to rotate thereby are the rotational-mass springs 162 andthe rotational mass 160. Relative rotational motion between thelinear-mass mounting plate 170 and the rotation-mass mounting plate 164is allowed by the mounting plate bearing 188. Relative rotational motionbetween the rotational mass 160 and the linear mass 166 is provided bythe rotation bearing 184 and relative linear motion between thetwomasses is provided by the linear bearing 186. A transition member 194separates the rotation bearing 184 from the linear bearing 186.

As was noted above in connection with FIGS. 4-7 the rotational-masssprings 162 and the linear-mass springs 168 are preloaded to somedegree, as can also be seen in the cutaway portion of FIG. 8. Theunloaded shapes of these springs are as shown in FIGS. 5 and 6. In thisregard, the springs are preloaded by screwing a threaded tensioningmember 196 onto the rotationalmass mounting plate 164. The tensioningmember 196 applies a force on the mounting plate bearing 188 which istransmitted to the linear-mass mounting plate 170, the linear-masssprings 168, the linear mass 166, the linear bearing 186, the transitionmember 194, the rotation bearing 184, the rotational mass 160, therotational-mass springs 162, back to the rotational-mass mounting plate164. The amount of tension applied to the springs 162 and 168 depends onthe extent to which the tensioning member 196 is screwed onto therotational-mass mounting plate 164. Normally the rotation of thetensioning member 196 is continued until the dimension A, in FIG. 7a isbetween 0.035 inches and 0.050 inches.

Dynamic seals 198 are attached to the rotationalmass mounting plate 164and the tensioning member 196 to prevent contaminants from entering theslippage sensor element 158.

In operation, the embodiment of the slippage sensor unit 158 shown inFIG. 8 functions substantially the same as the slippage sensor unitshown and described in connection with FIGS. 47. That is, when there isno unusual acceleration, the deformed springs 162 and 168 cause therotational mass and the linear mass 166 to press against one anotherthrough the rotation bearing 184, the transition member 194 and thelinear bearing 186. When, however, there is a disproportionate amount ofangular acceleration as compared to the linear acceleration adisproportionate amount of pressing force is created which causes linearmovement of the linear mass 166. This movement brings either theswitching magnet or the switching magnet 182 into a position in which itactivates a magnetic reed switch 64 or 66 (these switches are shown inthe FIG. 3 circuit).

The response time of the herein described automatic wheel brakingcontrol system is essentially the sum of the response times of: (l) theslippage sensing unit 158 (FIGS. 4 9); (2) the slippage sensor reedswitch 64 (FIG. 3); (3) the energizing relay 74 (FIG. 3); and (4) thelocking device 38 (FIG. 3).

Regarding the slippage sensing unit 158, the sensing masses do not waitto begin response until the degree of slippage which produces maximumefficiency is reached; but rather the movement of the masses, asrequired to activate the reed switch 64 shown in FIG. 3, actually beginsat virtually the instant the brakes are applied, and simply terminatesat the instant that the increasing slippage reaches the critical value.The sensor unit 158 and the reed switch 64 have a response time which,for practical purposes, is insignificant.

A solid-state relay is used as the energizing relay 74 because itsswitching action in response to an input signal is negligible for thepurposes of this system.

The fourth and last component to respond is the brake fluid lockingdevice 38. When the brakes of an automobile are applied, the brake fluidis in motion in the brake lines only until the brake lining contacts thebrake drum. At this time motion of the fluid ceases and its solefunction becomes that of transferring static pressure from the mastercylinder to the wheel cylinders. To take advantage of this, the plunger58 is always biased toward a seated position by its own weight. Thisbias is overcome by brake fluid flowing through the .valve toward thewheel cylinder. As a result, an unseating force is applied to theplunger only until the brake lining contacts the brake drum. At thisinstant the plunger 58 begins to settle back toward the seated positionso that, in the event of a panic stop, the solenoid need only beenergized and a positive seating of the plunger is virtuallyinstantaneously produced. This action isolates the wheel cylinder fromfurther increases in static pressure.

In summary, the total response time of the automatic traction controlsystem described above is extremely short, consequently should avehicles wheel reach some maximum braking efficiency slippage,regardless of its magnitude, the system is capable of stabilizing thebrake fluid pressure essentially at the value which creates the wheelslippage. This pressure is maintained constant until: (1) the motion ofthe wheel returns to rolling due to an increase in coefficient offriction; (2) the operator releases pressure on the brake pedal; or

(3) the vehicle comes to a complete stop. If any one or more of thepreceeding conditions develop, brake control is automatically returnedto the operator.

Another significant feature of the above described invention is that theslippage sensor unit detects both slippage due to braking a vehicle andaccelerating a vehicle and therefore can be used with both braking andaccelerating slippage control systems.

Still another advantageous feature of the above described system is thefact that it senses and controls the front and rear sets of wheelsindependently of one another.

It can be appreciated by those skilled in the art that the automatictraction control system described herein has been particularly describedand shown with reference to a preferred embodiment. It will beunderstood by those skilled in the art that various changes in form anddetail may be made therein without departing from the spirit and scopeof the invention. For example, the plunger 58 could be made of arelatively light material, in which case the solenoid valve supportspring 62 may not be necessary. Further, although the slippage sensorunit 158 (FIGS. 4-9) is illustrated and described herein forconventional drum type automobile brakes, its design can be altered tosatisfy other brake systems such as disc type brakes. In addition, therespective numbers of rotational-mass springs 162 and linear-masssprings 168 are shown in FIG. 4 to be four per sensor unit, however,this number can be altered. Also, the system described herein inconnection with an automobile can also be used with aircraft as well asother vehicles. In addition, the slippage detectors 36 a-d can be set toprovide slippage warning signals before the actual maximum-tractionefficiency point has been reached, as well as right at themaximum-traction efficiency point.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In a braking system of the type having a braking element which uponactivation of a brake pedal, is activated by fluid pressure applied tosaid braking element through a fluid line, an automatic braking devicecomprising:

a slippage detector means for detecting wheel slippage and for producingan actuating signal in response to a wheel slippage which is related toa maximum wheel-traction efficiency slippage;

a fluid-line locking means for locking said fluid line in response tosaid actuating signal and maintaining the fluid pressure applied to saidbraking element through said fluid line at a constant magnitude;

wherein said wheel slippage detector is of the type which compareslinear and angular accelerations of a wheel and comprises:

an angular accelerometer means rotating with said wheel for measuringthe angular acceleration of said wheel, said angular accelerometer meanscomprising first and second members which tend to move relative to oneanother in response to linear acceleration of said wheel;

wherein said first members of said angular and linear accelerometerspress against one another, each pressing with a force proportionate tothe respective acceleration being measured.

2. In a braking system of the type having a braking 6 element which uponactivation of a brake. pedal, is activated by fluid pressure applied tosaid braking element through a fluid line, an automatic braking devicecomprising:

a slippage detector means for detecting wheel slippage and for producingan actuating signal in responseto a wheel slippage which is related to a,maximum wheel-traction efficiency slippage;

a fluid-line locking means for locking said fluid line in response tosaid actuating signal and maintaining the fluid pressure applied to saidbraking element through said fluid line at a constant magnitude;

wherein said fluid-line locking means includes:

a valve which is ordinarily biased toward a closed position but which isopened by fluid flow in the direction of said braking element throughsaid fluid line; and

when a solenoid which when activated in response to an actuating signalcreates a force tending to hold said valve tightly in a closed position.

3. An automatic braking device as claimed in claim 2 wherein saidfluid-line locking means includes a bypass line for allowing fluid toflow freely away from said braking element, bypassing said valve.

4. An automatic braking device as claimed in claim 3 wherein saidslippage detector means is of the type which compares linear and angularaccelerations of a wheel and comprises:

an angular accelerometer means rotating with said wheel for measuringthe angular acceleration of 1 said wheel, said angular accelerometermeans comprising first and second members which tend to move relative toone another in response to angular acceleration of said wheel; and

a linear accelerometer means for measuring the linear acceleration ofsaid wheel, said linear accelerometer means comprising first and secondmembers which tend to move relative to one another in response to linearacceleration of said wheel,;

wherein said first members of said angular and linear accelerometerspress against one another, each pressing with a force proportionate tothe respective acceleration being measured.

5. An automatic braking device as claimed in claim 2 wherein the extentto which said valve is biased toward a closed position is relativelyslight so that a relatively insignificant pressure differential acrosssaid valve is required to open said valve when said solenoid is notenergized.

6. An automatic braking device as claimed in claim 5 wherein said valveis gravity biased but wherein is further included a gravity counteringmeans for reducing the effects of said gravity.

7. In an automatic braking system of the type having a braking elementwhich is activated by fluid pressure applied to said braking elementthrough a fluid line, an automatic braking device comprising:

a slippage detector means for detecting wheel slippage and for producingan actuating signal in response to a wheel slippage which is related toa maximum wheel-traction efficiency slippage;

a fluid-line locking means for locking said fluid line in response tosaid actuating signal, said fluid-line locking means including:

a valve means including a valve element and a gravity biasing means forallowing gravity to ordinarily bias said valve element in a closedposition but which is opened by fluid flow in the direction of saidbraking element through said fluid line; and

a solenoid which when activated in response to said actuating signalcreates a force tending to hold said valve tightly in the closedposition.

8. An automatic braking system as claimed in claim 7 wherein saidfluid-line locking means includes a bypass means for allowing fluid toflow freely away from said braking element, bypassing said valve.

9. An automatic braking device as claimed in claim 7 wherein the extentto which said valve is gravity biased toward a closed position isrelatively slight so that a relatively insignificant pressuredifferential across said valve is required to open said valve when saidsole noid is not energized.

10. An automatic braking device as claimed in claim 9 wherein saidgravity biasing means further includes a gravity countering means forcountering the effects of said gravity bias toward a closed position.

11. An automatic braking device as claimed in claim 7 wherein said wheelslippage detector is of the type which compares linear and angularacceleration of a wheel and comprises:

an angular accelerometer means rotating with said wheel for measuringthe angular acceleration of said wheel, said angular accelerometer meanscomprising first and second members which tend to move relative to oneanother in response to angular acceleration of said wheel;

a linear accelerometer means for measuring the linear acceleration ofsaid wheel, said linear accelerometer comprising first and secondmembers which tend to move relative to one another in response to linearacceleration of said wheel;

wherein said first members of said angular and linear accelerometerspress against one another, each pressing with a force proportionate tothe respective acceleration being measured.

1. In a braking system of the type having a braking element which uponactivation of a brake pedal, is activated by fluid pressure applied tosaid braking element through a fluid line, an automatic braking devicecomprising: a slippage detector means for detecting wheel slippage andfor producing an actuating signal in response to a wheel slippage whichis related to a maximum wheel-traction efficiency slippage; a fluid-linelocking means for locking said fluid line in response to said actuatingsignal and maintaining the fluid pressure applied to said brakingelement through said fluid line at a constant magnitude; wherein saidwheel slippage detector is of the type which compares linear and angularaccelerations of a wheel and comprises: an angular accelerometer meansrotating with said wheel for measuring the angular acceleration of saidwheel, said angular accelerometer means comprising first and secondmembers which tend to move relative to one another in response to linearacceleration of said wheel; wherein said first members of said angularand linear accelerometers press against one another, each pressing witha force proportionate to the respective acceleration being measured. 2.In a braking system of the type having a braking element which uponactivation of a brake pedal, is activated by fluid pressure applied tosaid braking element through a fluid line, an automatic braking devicecomprising: a slippage detector means for detecting wheel slippage andfor producing an actuating signal in response to a wheel slippage whichis related to a maximum wheel-traction efficiency slippage; a fluid-linelocking means for locking said fluid line in response to said actuatingsignal and maintaining the fluid pressure applied to said brakingelement through said fluid line at a constant magnitude; wherein saidfluid-line locking means includes: a valve which is ordinarily biasedtoward a closed position but which is opened by fluid flow in thedirection of said braking element through said fluid line; and when asolenoid which activated in response to an actuating signal creates aforce tending to hold sAid valve tightly in a closed position.
 3. Anautomatic braking device as claimed in claim 2 wherein said fluid-linelocking means includes a bypass line for allowing fluid to flow freelyaway from said braking element, bypassing said valve.
 4. An automaticbraking device as claimed in claim 3 wherein said slippage detectormeans is of the type which compares linear and angular accelerations ofa wheel and comprises: an angular accelerometer means rotating with saidwheel for measuring the angular acceleration of said wheel, said angularaccelerometer means comprising first and second members which tend tomove relative to one another in response to angular acceleration of saidwheel; and a linear accelerometer means for measuring the linearacceleration of said wheel, said linear accelerometer means comprisingfirst and second members which tend to move relative to one another inresponse to linear acceleration of said wheel; wherein said firstmembers of said angular and linear accelerometers press against oneanother, each pressing with a force proportionate to the respectiveacceleration being measured.
 5. An automatic braking device as claimedin claim 2 wherein the extent to which said valve is biased toward aclosed position is relatively slight so that a relatively insignificantpressure differential across said valve is required to open said valvewhen said solenoid is not energized.
 6. An automatic braking device asclaimed in claim 5 wherein said valve is gravity biased but wherein isfurther included a gravity countering means for reducing the effects ofsaid gravity.
 7. In an automatic braking system of the type having abraking element which is activated by fluid pressure applied to saidbraking element through a fluid line, an automatic braking devicecomprising: a slippage detector means for detecting wheel slippage andfor producing an actuating signal in response to a wheel slippage whichis related to a maximum wheel-traction efficiency slippage; a fluid-linelocking means for locking said fluid line in response to said actuatingsignal, said fluid-line locking means including: a valve means includinga valve element and a gravity biasing means for allowing gravity toordinarily bias said valve element in a closed position but which isopened by fluid flow in the direction of said braking element throughsaid fluid line; and a solenoid which when activated in response to saidactuating signal creates a force tending to hold said valve tightly inthe closed position.
 8. An automatic braking system as claimed in claim7 wherein said fluid-line locking means includes a bypass means forallowing fluid to flow freely away from said braking element, bypassingsaid valve.
 9. An automatic braking device as claimed in claim 7 whereinthe extent to which said valve is gravity biased toward a closedposition is relatively slight so that a relatively insignificantpressure differential across said valve is required to open said valvewhen said solenoid is not energized.
 10. An automatic braking device asclaimed in claim 9 wherein said gravity biasing means further includes agravity countering means for countering the effects of said gravity biastoward a closed position.
 11. An automatic braking device as claimed inclaim 7 wherein said wheel slippage detector is of the type whichcompares linear and angular acceleration of a wheel and comprises: anangular accelerometer means rotating with said wheel for measuring theangular acceleration of said wheel, said angular accelerometer meanscomprising first and second members which tend to move relative to oneanother in response to angular acceleration of said wheel; and a linearaccelerometer means for measuring the linear acceleration of said wheel,said linear accelerometer means comprising first and second memberswhich tend to move relative to one another in response to linearacceleration of said wheel; wherein said first members of said angularand linear accelerometers press against one another, each pressing witha force proportionate to the respective acceleration being measured.